Preparation

• Melt 2 Tbs. of the butter in a 10-inch straight-sided sauté pan over medium heat. Add the potatoes and enough water to just cover them (about 2 cups). Bring to a boil. Add 1 tsp. salt, cover the pan, reduce the heat to medium low, and cook, shaking the pan occasionally, until the potatoes are just tender, about 8 minutes. Uncover the pan, raise the heat to medium high, and add the remaining 2 Tbs. butter. Cook, shaking the pan occasionally, until all of the liquid has reduced to a glaze and the potatoes are lightly browned, about 20 minutes more.
• Meanwhile, cook the pancetta in an 8-inch nonstick skillet over medium heat, stirring occasionally, until crisp, 6 to 8 minutes. Transfer to a paper-towel-lined plate. Pour off any fat from the pan, return the pan to medium heat, and add 1/2 Tbs. of the oil. Add the shallot to the pan and cook, stirring, until tender, about 2 minutes. Stir in the vinegar and mustard and cook until the mustard is smooth, 30 seconds to 1 minute. Transfer the mixture to a small bowl and gradually whisk in the remaining 4-1/2 Tbs. oil. Season to taste with salt and pepper.
• 把莴苣菜和肉在一个大碗里toss with 3 Tbs. of the vinaigrette. Season to taste with salt and pepper. Divide the salad and the potatoes among 4 salad plates and sprinkle with the cheese. Drizzle with the remaining vinaigrette and serve.